Dual functions of yeast tRNA ligase in the unfolded protein response: unconventional cytoplasmic splicing of HAC1 pre-mRNA is not sufficient to release translational attenuation.
Dual functions of yeast tRNA ligase in the unfolded protein response: unconventional cytoplasmic splicing of HAC1 pre-mRNA is not sufficient to release translational attenuation.
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DOI：
10.1091/mbc.e10-08-0693
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发表时间：
2010-11-01
影响因子：
3.3
通讯作者：
Yoshihisa T
中科院分区：
文献类型：
--
作者：
Mori T;Ogasawara C;Inada T;Englert M;Beier H;Takezawa M;Endo T;Yoshihisa T
非常规胞质剪接的HAC 1 mRNA是必不可少的酵母未折叠蛋白反应（UPR）。UPR需要对未剪接和剪接形式的HAC 1 mRNA进行翻译调控。在这里，我们报告的tRNA连接酶，Rlg 1 p，连接的HAC 1外显子在其剪接，有另一个面孔作为一个翻译调控的HAC 1 mRNA。未折叠蛋白反应（UPR）是内质网中科普蛋白折叠应激的重要信号转导途径。在酵母UPR中，HAC 1 mRNA的非常规剪接是关键步骤。HAC 1前mRNA（HAC 1u mRNA）的翻译在多核糖体上减弱，仅在UPR剪接后重新开始。然而，这种重启的确切机制仍不清楚。在这里，我们表明，酵母tRNA连接酶（Rlg 1 p/Trl 1 p）作用于HAC 1连接有一个意想不到的作用，在HAC 1翻译。来自拟南芥的RLG 1同源物（AtRLG 1）在tRNA剪接中取代酵母RLG 1，但在UPR中不取代。令人惊讶的是，AtRlg 1 p连接HAC 1外显子，但剪接的mRNA（HAC 1 i mRNA）不能有效翻译。在AtRLG 1细胞中，HAC 1内含子在剪接后被环化，并保持与多核糖体相关，从而削弱了对HAC 1 i mRNA翻译抑制的缓解。此外，HAC 1 5′ UTR本身使酵母Rlg 1 p能够调节以下ORF的翻译。RNA IP显示，在Ire 1 p切割HAC 1u mRNA之前，酵母Rlg 1 p整合在HAC 1 mRNP中。这些结果表明，剪接和释放的HAC 1 mRNA的翻译衰减是可分离的步骤，Rlg 1 p在这两个步骤中具有关键作用。
Unconventional cytoplasmic splicing of HAC1 mRNA is essential for the yeast unfolded protein response (UPR). The UPR requires translational regulation of unspliced and spliced forms of HAC1 mRNAs. Here we report that tRNA ligase, Rlg1p, which ligates HAC1 exons in its splicing, has another face as a translational regulator of HAC1 mRNA. The unfolded protein response (UPR) is an essential signal transduction to cope with protein-folding stress in the endoplasmic reticulum. In the yeast UPR, the unconventional splicing of HAC1 mRNA is a key step. Translation of HAC1 pre-mRNA (HAC1u mRNA) is attenuated on polysomes and restarted only after splicing upon the UPR. However, the precise mechanism of this restart remained unclear. Here we show that yeast tRNA ligase (Rlg1p/Trl1p) acting on HAC1 ligation has an unexpected role in HAC1 translation. An RLG1 homologue from Arabidopsis thaliana (AtRLG1) substitutes for yeast RLG1 in tRNA splicing but not in the UPR. Surprisingly, AtRlg1p ligates HAC1 exons, but the spliced mRNA (HAC1i mRNA) is not translated efficiently. In the AtRLG1 cells, the HAC1 intron is circularized after splicing and remains associated on polysomes, impairing relief of the translational repression of HAC1i mRNA. Furthermore, the HAC1 5′ UTR itself enables yeast Rlg1p to regulate translation of the following ORF. RNA IP revealed that yeast Rlg1p is integrated in HAC1 mRNP, before Ire1p cleaves HAC1u mRNA. These results indicate that the splicing and the release of translational attenuation of HAC1 mRNA are separable steps and that Rlg1p has pivotal roles in both of these steps.